I pulled every best-of-7 NHL playoff series from Hockey-Reference spanning 1987–present and broke down series win probability by series state, home/away status of the game winner, and momentum context. Sample sizes vary significantly by state so I've included n(#) values throughout.
Base Rates - Series win probability by Series State
I chose this as a starting point so I can layer in some home/away context later. The 3–0 row (n=211) is essentially a closed question at 98.1%. More interesting are the mid-series states where variance is highest 1–0 (68.1%, n=788) and 2–1 (69.0%, n=574) have nearly identical win probabilities despite representing different series trajectories.
Game 1 - Home/Away Split
Home team winning G1: 74.7% series win rate (n=370). Away team winning G1: 56.8% (n=167). The ~18 point gap is the largest home/away differential of any individual game in the dataset. Worth noting the sample skews heavily toward home G1 wins, which is expected given home ice advantage in Game 1.
Game 3 - Road Momentum Effect
The 1–1 tied state is the most analytically interesting here. Road team winning G3 from 1–1: 70.0% series win rate (n=133) vs home team at 62.4% (n=111). The road winner actually outperforms despite taking a 2–1 lead being equivalent in both cases — the only difference is home/away context.
The 0–2 state has the thinnest samples (n=33 home, n=21 away) so those numbers should be treated cautiously.
Game 5 - Closing vs Survival
Game 5 from a 2-2 tie is the one scenario where home teams show a meaningful edge in a high=leverage situation; 80.6% (n=150) vs 77.4% (n=89) for road winners. The 1–3 survival scenarios are small samples (n=15 and n=17) and probably shouldn't be over-interpreted.
Game 7 - Home Ice Disappears
The most notable finding in the dataset. Home teams in Game 7 win the series just 46.8% of the time (n=94) vs 53.2% for road teams (n=107). Home ice advantage, while meaningful in every other context, doesn't seem to provide any sort of boost to the home team.
Breaking it down by G6 outcome adds another layer: teams that won G6 on the road go on to win G7 at 57.1% (n=70), compared to 41.2% (n=131) for teams that won G6 at home. Road momentum heading into G7 appears to be the strongest single predictor in the whole dataset.
All data collected from Hockey Reference